DE2721169C2 - Process and system for processing thermoplastics or thermosets - Google Patents

Description

The invention relates to a method for processing thermoplastics or thermosets according to the preamble of claim 1.

To carry out such a process is from the magazine "Kunststoffe", 1968, issue 8, pages 544 to 546 a double mixer known, which consists of an upper heating mixer and a lower cooling mixer be The heating mixer has a stage mixer that ensures the necessary, intensive vertical circulation The heating takes place via a continuous oil heater in the double jacket of the heating / mixing tank. The processing takes place primarily through externally supplied heat me, but also unavoidable due to frictional heat. The material to be processed is made of a silo by means of a dosing screw into an intermediate storage container of a scale, which If the desired amount is reached, the dosing screw switches off. Another silo is then turned off by means of a further metering screw, an aggregate or a mixture of aggregates is added to the intermediate storage container of the balance, whereby also the second metering screw is switched off after the desired weight has been reached. The total batch of the material to be processed, including aggregates, must be stored in the intermediate storage container The scales must be ready, weighed, before the loading Dispatch of the heating mixer can begin. The pure ones Filling times of 10 to 20 seconds are definitely lost times in this known system. Since with this known system only 7 to 8 batches per hour are processed, d. H. because the total batch time is about 7.5 to 3 minutes, these lost times are not very important.

Since in processes of the generic type in which the preparation of the materials exclusively the batch times are very much due to frictional heat are much shorter, times for dosage and fall Adding the material much more heavily into the weight

The invention is based on the object of developing the method of the generic type so that a shortening of the cycle times for dosing and Addition of the material is achieved with a view to short batch times.

This object is achieved in a method of the generic type by the features in the characterizing part of claim t The essence of the invention The reason for this is that a batch-wise device is acted upon by a continuous flow of material which is merely corresponding the cycle times are temporarily stored and then suddenly entered into the container in batches. the This eliminates the total addition times. The batch time within which a batch is prepared is here shorter than the cycle time within which a batch is continuously dosed, so that continuous dosing never occurs at any time

so must be interrupted. The process according to the invention has made it possible to greatly increase the batch times to reduce. From this, however, it again follows that for a given amount of material to be processed per Time unit the size of the device to be used can be significantly reduced.

If conventional plastics processing machines are arranged downstream, devices for the preparation of thermoplastics or thermosets can be used, which are about laboratory size, i.e. a

Volume of the container of 2 or 3 liters.

If liquid is also to be added to the device, then the further development according to claim 2 is advantageous. Of course, the liquid does not have to be added at the same time as the tend to be made of material; it can, for example, only take place during the preparation of the material.

By the development according to claim 3, according to the after emptying the device during

of the previous cycle temporarily stored amount of material with still running mixing tools in the device is entered, there are also no lost times for starting or stopping the device.

A system for performing the method with the features of the preamble of claim 4 is Advantageous embodiments characterized by the features in the characterizing part of claim 4 result from claims 5 to 7.

The cycle times of the system are in principle completely independent of the batch times, whereby, of course, in practice, care is taken that none are too There are long dead times between the batch times and the cycle times, i.e. after ejection one Batch from the device there is no dead time that is too long until the next batch is dosed and into the Container of the device can be abandoned. As materials, i.e. H. come as plastic raw materials especially those in powdery, givnulate form, but also in paste-like consistency into consideration. It is crucial that these materials still exist at all are accessible to continuous dosing.

The invention is explained by means of an exemplary embodiment with reference to the drawing. In the drawing shows

F i g. 1 a system for processing thermoplastics or thermosets in a schematic representation,

F i g. 2 diagrams showing the dosing of the material, the input of the material and the preparation of the Materials show over time, and

F i g. 3 shows the performance over time.

At the lower end of a storage bunker 1, in which by means of level sensors 2, 3 within the through The latter is one of the limits that a filling with the material to be reprocessed is maintained arranged volumetrically operating metering device, which consists of a metering screw arranged in a housing 4 5 consists The metering screw 5 is driven by a drive motor 6 via a continuously adjustable Gear 7 driven. By means of this metering device, a continuous volume flow of the Material withdrawn from the storage bunker 1. This continuous volume flow is over a gravimetric control device connected downstream of the volumetrically operating metering device out, which consists of a belt scale 8 in the present case. In the event of fluctuations in the volume flow (weight flow) per unit of time that is displayed on a display device 9 of the belt scale 8, the of the material flow coming from the volumetrically operating metering device by adjusting the gear 7 be changed either by hand or by suitable control devices in such a way that in any case by the gravimetric control device (belt scale 8) a continuous mass flow, d. H. constant material weight quantities per unit of time, falls via a fall line 10 into an intermediate storage container 11. This intermediate storage container 11 is at its bottom with a closure device in the form of a closure slide 12 lockable, which by means of a suitable drive, for example a hydraulic or pneumatic working cylinder 13, can be opened or closed very quickly.

The intermediate storage container 11 is via a feed nozzle 14 a device 15 for processing thermoplastics or thermosets is arranged downstream. It has an essentially cylindrical container 16, in which an rPit mixing tools 17 are occupied The shaft 18 is arranged concentrically and is supported in bearings 19, 20. The container 16 is complete at one end closed with an end wall 21, which only has a corresponding passage for the shaft 18 At the other end, the shaft 18 is led out through an end wall 22 which has a passage opening 23 has. On the section upstream of this passage opening 23 is the shaft with a screw conveyor 24, which is arranged in the bottom area of the feed connector 14 in the lower area of the container 16, an emptying flap 25 is provided, which is via a lever 26, which is attached to one in the machine frame 27 mounted shaft 28 is fixed can be opened or closed. A hydraulic working cylinder is required for this 29 provided, the working piston 30 at an eccentric at the associated end of the shaft attached toggle lever 31 engages.

Nozzles 32 are attached in the container wall. Furthermore, a liquid storage container 33 is provided, from which a line 34 leads to an intermediate liquid vessel 35, which is designed as a pressure vessel. In the line 34 a metering pump 36 is connected, which is controlled by a drive motor 37 via a continuously variable Gear 38 is driven. The intermediate liquid vessel 35 consists of a cylindrical container 39, in which a piston 41 loaded from above by a pretensioned compression spring 40 is arranged displaceably is. The line 34 opens into the container 39 at the bottom. A check valve 42 is also in the line 34 arranged. From the bottom of the container a line 43 leads out to the nozzles 32, in which a means a hydraulic drive 44 actuatable quick-closing valve 45 is switched. The intermediate storage container 11 and the intermediate liquid vessel 35 can each have a section extending over their height 46 and 47 have made of transparent material on which a level scale is attached, the one Optical control of the ones in the intermediate storage container 11 or the intermediate liquid vessel 35 Allow material or liquid quantities.

The drive of the shaft 18 of the device for processing thermoplastics and thermosets takes place by a continuously rotating drive motor 48 with the interposition of a hydrodynamic gear 49, i.e. a hydrodynamic torque converter, and a continuously variable transmission 50.

The mode of operation of the system is illustrated using the diagrams in FIG. 2 explained. From the storage bin 1, a f over the time constant stream ΠΊα, Μαπ (see is given curve a ^ to the buffer reservoir U by means of the volumetrically operating metering device and gravimetric control, the closure slider 12 is closed in this case. According to the curve b increases in the intermediate storage tank 11 amount of material contained in the time of ίο to t \ of 0 to a predetermined amount rri \ in. Then, it is opened by means of the working cylinder 13 of the lock slider 12 abruptly, so that the total amount m \ falls from the intermediate storage tank 11 into the feed pipe 14 Immediately after this emptying process has been completed, the slide gate 12 is closed again. Of course, during this emptying process, material continues to be fed in in a continuous flow according to curve a , which then falls directly into the feed nozzle 14. Overall, when the slide valve opens, the in the period from ίο until i> quantity requested in a continuous stream;? J: in the feed nozzle 14. Zur

Time f2 the closure slide is closed again. The period from ii to ti is very small in relation to the time from to to fi. This process is repeated continuously. The time from ta to h is the cycle time T of the entire system. As already mentioned, the shaft 18 of the device 15 rotates continuously so that the material arriving in the feed nozzle 14 in the period from U to t _{2 is given} by the screw conveyor 24 almost without delay into the container 16, where it is subjected to a treatment . At the end of the treatment, at time ti, the emptying flap 25 is opened by means of the working cylinder 29 and the finished material is ejected. This emptying process is completed at time U. The time from t \ to U is the batch time Tc of the device 15. This batch time Tc must in any case be slightly shorter than the cycle time Γ of the intermediate storage container U.

The last-mentioned times are shown in curve c in FIG. 2 shown.

In principle, the liquid is supplied in the same way. The metering pump 36 works continuously and fills the intermediate liquid vessel 35 in the time from fo to t \ with a corresponding displacement of the piston 41 with additional biasing of the spring 40. At the time t \ the quick-action valve 45 is opened, whereby the amount of liquid in the container 39 is under The spring 40 is released in a very short time, for example until the nozzle 32 is sprayed into the container 16 at the point in time f *. The check valve 42 prevents a liquid backlash into the line 34 from occurring. The amount of liquid conveyed by the metering pump 36 in the cycle time 7 ″ is thus entered into the container 16 within one cycle, these cycles being able to be offset in time with respect to the cycles of the intermediate storage container 11.

As material supplied from the storage bunker 1 Serve thermoplastics or thermosetting plastics in powder form, which are already filled with dyes, fillers or the like are premixed. Plasticizers are used as the liquids supplied from the liquid storage container 33 or similar. This material, which if applicable the liquid is added, is due in the device 15 in a known manner by the during operation the rotation of the shaft 18 with mixing tools 17 gels and, if necessary, internal frictional heat granulated. This process and this device 15 per se have been known for a long time and are commercially available.

In Fig. 3, the power N is plotted against time in curve d ! Which is to be generated by the drive of the device 15 when the shaft 18 is driven at a constant speed. As can be seen from this curve, the power N rises at first very flat and then relatively steeply until it reaches a maximum value. Here, it remains approximately constant for a short period of time, the softening of the materials are to be treated corresponds to the area under the curve d, the total work done by the material and substantially! work that has been taken up and converted into heat again.

If - according to curve e - an approximately constant power is introduced into the material over time, then the work required to prepare the material is introduced into the material in a much shorter time, namely the batch time 7c, ie the batch time Tc with the latter type of drive much shorter than with the drive with constant speed. Correspondingly, the speed of the shaft 18 drops from an extremely high value at the beginning of the batch time to a correspondingly lower value at the end of the batch time 7 "c-.

Instead of the joint supply of plastic raw materials that have already been premixed with dyes, fillers or the like by means of a metering device, several continuously operating metering devices can also be used be provided that the various additives also continuously with in the intermediate storage container 11 metering, the individual metering devices being naturally coupled to one another must be.

The shaft 18 rotates at such a speed that the mixing tools 17 have a peripheral speed from 20 to 100 m / sec.

For this purpose 2 sheets of drawings

Claims (7)

Patent claims: 1. Process for processing thermoplastics or thermosets using a batch-wise device with high-speed drivable mixing tools, in which the material to be processed and, if necessary, liquid is temporarily stored in doses and fed to the device in a weighed amount, processed by frictional heat and then removed from the device Device is ejected, characterized in that the material in an over several batch cycles uninterrupted, gravimetrically controlled constant volume flow is fed to the intermediate storage. 2. The method according to claim 1 with Fiüssigkeitszugahe, characterized in that the liquid in a continuous, constant volume flow of an intermediate storage and during Batch time of the material to be processed is entered cyclically into the device at predetermined time intervals. 3. The method according to claim 1 or 2, characterized in that the supply of the temporarily stored materials takes place with the mixing tools running 4. Plant for performing the method according to one of claims 1 to 3, with a device, which has a cylindrical container with high-speed drivable mixing tools arranged coaxially in it, with a continuously drivable volume metering device, which has a the intermediate storage container connected to the container of the device is arranged downstream, and with a weighing device, characterized in that the metering device (5) can be driven continuously and that the weighing device (8) is designed as a gravimetric control device for the metering device (5) and is arranged between the metering device (5) and the intermediate storage container (II). 5. Plant according to claim 4, characterized in that the device (15) has a continuously operating metering pump (36) for liquid with a downstream intermediate liquid vessel (35) which feeds the liquid cyclically into the device (15). 6. Plant according to claim 5, characterized in that the intermediate liquid vessel (35) as Pressure vessel is formed. 7. Plant according to one of claims 4 to 6, characterized in that the intermediate storage container (11) one in the container (16) of the device (15) opens, fixed to the shaft (18) of the Mixing tools (17) connected to the screw conveyor (24) is arranged downstream.